Drug addiction remains a major public health issue. Addiction is characterized by lack of inhibitory control over drug seeking. Periods of remission, in which inhibitory control returns, are punctuated by relapses to active addiction. However, skills learned during behavioral therapies can protect against relapses. Investigation of the synaptic plasticity mechanisms underlying inhibitory learning may enable enhancement of inhibitory control by novel therapies. However, the relatively limited understanding of synaptic plasticity underlying extinction in drug seeking has precluded successful therapies to augment extinction learning. Hence, this proposal outlines a series of experiments that will determine the role of transient synaptic potentiation (t-LTP) in the infralimbic (IL) to accumbens shell (NAshell circuit in extinction from cocaine. Our preliminary data demonstrates t-LTP in dendritic spine head diameter in NAshell during an extinction session, meaning that spine head diameter rapidly (15 min) increases and then normalizes by 45 min. We hypothesize that electrophysiological t-LTP will be confined to NAshell during extinction and to NAcore during reinstatement. We further hypothesize that the IL to NAshell circuit is necessary and sufficient for extinction and associated t-LTP. These hypotheses, based upon preliminary data, will be tested through two specific aims. Aim 1 will employ patch clamp electrophysiology to determine the time course of changes in AMPA:NMDA ratio during extinction and reinstatement in NAshell and NAcore. Aim 2 will employ a DREADD (Designer Receptor Exclusively Activated by Designer Drug) strategy to determine the role of the IL to NAshell circuit in extinction-associated t-LTP. In addition to clarifying the role of transient corticostriatal synaptic plasticity in extintion from cocaine, this fellowship will train the applicant in modern techniques for manipulating neural circuits and assessing synaptic potentiation.